A wireless network may comprise an access point and at least one client device. The access point may be coupled to a network, such as the Internet, and enable the client device to communicate via the network (and/or communicate with other devices coupled to the access point). Generally, the wireless access point may send data to the at least one client device in the form of one or more frames. To reduce power consumption, a client device may operate in a low power consumption mode (e.g., a sleep mode) in some circumstances, such as when the client device is not being used for communications (e.g., with the access point). Under the IEEE 802.11X (e.g., 802.11b, 802.11g, 802.11n) standards for WI-FI communications, a client device may periodically awake from a low power consumption mode, and receive a beacon from an access point. The beacon may include information regarding present or future communications between the client device and the access point. According to one example, the beacon may include information such as a traffic indication map (TIM) and/or a delivery traffic identification message (DTIM) information elements (IE) that indicates whether frames of data are waiting to be communicated to the client device. Further, the beacon may also contain other information pertinent to the operation of the network, delivered as an IE or in other suitable manners.
To provide further power saving advantages, techniques have been developed to maximize time spent in low power mode, allowing the device to return to a low power mode of operation before an entire beacon is received by the client device. For example, a client device may awake from a low power mode of operation to receive a first portion of a beacon. As discussed above, a portion of the beacon may include information related to communications with the access point, such as an indication of whether one or more frames of data are forthcoming from the access point (e.g., waiting to be sent to the client device). In some embodiments, this information is contained in the DTIM. If the information from the access point indicates no frames of data are forthcoming, the client device preferably returns to a low power consumption mode of operation before receiving subsequent portions of the beacon. As will be appreciated, such techniques allow the client device to spend a greater portion of time in low power mode, reducing the overall power consumption associated with access point communications. Such strategies are generally referred to herein as early beacon termination (EBT) techniques and are known in the art.
Despite the power saving advantages represented by EBT techniques, it would be desirable to optimize certain performance aspects. Typically, wireless communication devices are designed so that important system parameters will not be updated on the basis of a received frame unless the integrity of that frame can be confirmed. One example is the time synchronization function (TSF) used to keep the clocks on the client device and the access point coordinated. Since synchronization is critical to proper functioning, the client device will not update its TSF unless there is reasonable confidence in the validity of the timing information transmitted by the access point. However if the client device is not able to validate the TSF for a sufficient period of time, clock drift that affects each device may result in the client device being out of synchronization with the access point, impairing performance. Another important system parameter relates to coordinated channel switching involving the access point and a client device. The access point may indicate an imminent switch to a different channel, such as to avoid interference, using the channel switch announcement (CSA) IE. Since transmission will be interrupted if the client device switches channels erroneously, it is generally desirable to have a high degree of confidence in the validity of the CSA IE before implementing a switch.
Positioning of the DTIM within the beacon may not be mandated by the wireless specifications, but often occurs relatively early and before validation information which typically comes towards the end of transmissions. In the IEEE 802.11X protocols, for example, frames end with a frame check sequence (FCS) IE that allows the client device to verify the integrity of the received frame. Similarly, other network information may also be contained in the beacon and positioned at various point relative to the FCS. Accordingly, when a period time elapses during which the access point has no frames to transmit to the client device, EBT will result in the client device returning to low power mode before the FCS. In turn, information transmitted by the access point cannot be verified and parameters such as TSF and CSA may not be updated. System parameters relying on other network information may be similarly affected.
Another aspect of the impact of EBT strategies results from the architecture of the beacon frame. As noted earlier, IEEE 802.11X protocols generally result in the DTIM occurring relatively early in the beacon frame. This is followed by a variable number of additional IEs and finally by the FCS. As a practical matter, channel conditions change constantly in a typical wireless communication system. Thus, there are situations in which the channel is good enough for valid reception during the DTIM, but the quality will erode over the successive IEs and ultimately fail the FCS. This may occur when the time between the DTIM and the FCS exceeds the coherence time of the channel or if there is a deep fade in the signal during the period. While the former may be equalized to some extent by efficient pilot interpolation, which is optionally applied due to varying degrees of implementation complexities, the latter would certainly result in irrecoverable errors and lead to FCS failures. Under prior EBT mechanisms, the client device simply discards the frame even though the DTIM was set because the channel has degraded to the point that the FCS fails, even though the DTIM or other network information may have been received while the channel was still valid. Correspondingly, under such situations, the performance of the client device will suffer since it is disregarding valid data, such as missing the opportunity to respond to the access point with a power save poll (PS-POLL) to enable the access point to deliver waiting frames to the client device or failing to update important system parameters.
Accordingly, it would be desirable to provide a wireless communication system that features the power saving benefits represented by an EBT function while minimizing the impact on performance. To that end, it would be desirable for a client device to be able to update important system parameters even when the client device is not receiving a beacon transmission in its entirety. It would also be desirable to provide such a wireless communication system that can utilize a valid DTIM or other IE even when the channel degrades over time and causes the FCS to fail. This disclosure is directed to systems and methods that accomplish these and other goals.